Marine mud hydrocarbon surveying

ABSTRACT

A process for exploring a water-covered region is improved by jetting water into soft bottom sediments, forming a slurry of the sediments in water, extracting gas from the slurry and measuring the concentration with location of a mobile reservoir fluid that was entrapped within the bottom sediments.

United States Patent 91 Daigle et a1.

[ 1 MARINE MUD HYDROCARBON SURVEYING [75] Inventors: Edwin E. Daigle;Robert R. Luke; James B. Turner; Harold L. Wise, all of Houston, Tex.

[73] Assignee: Shell Oil Company, New York, NY.

[22] Filed: June 22, 1970 [21] Appl. No.: 48,366

[ Feb. 6, 1973 2,346,203 4/1944 Zaikowsky 175/60 X 2,774,569 12/1956.lacobsen 3,486,570 12/1969 Richardson....

3,490,550 l/1970 Horton ..175/213 X OTHER PUBLICATIONS Abstract No.107857, Petroleum Abstracts 1969,

Libby et 211.; How To Carry Out An Efficient Program For SamplingOff-Shore Minerals," Eng. Mining 1., Vol. 169, No. 12, pp. 72-74,December, 1968.

Primary Examiner-Richard C. Queisser Assistant Examiner-C. E. Snee, IIIAttorney-Harold W. Coryell and Harold L. Denkler [57] ABSTRACT A processfor exploring a water-covered region is improved by jetting water intosoft bottom sediments, forming a slurry of the sediments in water,extracting gas from the slurry and measuring the concentration withlocation of a mobile reservoir fluid that was entrapped within thebottom sediments.

8 Claims, 4 Drawing Figures GAS DISCHARGE GAS GAS EXTRACTOR ANALYZER l-l2o 2' -16 -::t'.:-: t T; g SLURRY r DISCHARGE RECORDER ETHANE TOTALHYDRO- CARBON GAS DISCHARGE GAS GAS EXTRACTOR ANALYZER I USILURRT ','-|5

DISCHARGE RECORDER ETHANE TOTAL HYDRO- CARBON /2/ETHANE ?/--OFF-SCALETOTAL HYDROCARBON Nina - INVENTORS: FIG. I EDWIN E. DAIGLE ROBERT R.LUKE JAMES B. TURNER HAROLD L.WISE

THEIR ATTORNEY PATENTEUFEB 6|975 3,714,811

SHEET 2 [IF 2 FIG. 4

INVENTORS:

EDWIN E. DAIGLE ROBERT R. LUKE JAMES B. TURNER HAROLD L.WISE

THEIR ATTORNEY 1 MARINE MUD HYDRO CARBON SURVEYING BACKGROUND OF THEINVENTION The invention relates to a process for investigating earthformations located under a large body of water. More particularly itrelates to measuring the concentration with location of a mobilefluid,-such as a hydrocarbon, in sediments at the bottom of a body ofwater, in order to locate an underlying reservoir that contains themobile fluid,.

Mobile reservoir fluids, such as hydrocarbons and/or inorganic gases,are known to seep from subterranean reservoirs and migrate up throughthe overlying earth formations. Priorprocedures for exploringwatercovered regions have utilized various combinations of geophysicaltechniques, such as seismic or gravity mapping techniques, andmeasurements of the amounts of hydrocarbon and/or inorganic gases in abody of water or in core samples or bit cuttings of the earth formationsunderlying the water. The obtaining of core samples or bit cuttings is arelatively expensive operation and is usually employed only in locationsthat have been selected as the sites for wells, or platforms, or thelike.

A survey or map of the amount with location of a mobile reservoir fluidthat might be contained within a body of water is not significant unlessthe bottom. sediments have allowed the reservoir fluid to flow throughthem and enter the water. In a region containing subterranean structureshaving geophysical properties that may be indicative of a subterraneanreservoir, the overlying water may be substantially devoid of any mobilereservoir fluid. Such a situation is common when the bottom sedimentsare soft and relatively impermeable, such as the clays or muds thatcover much of the Gulf of Mexico. An absence of hydrocarbons in thewater above a subterranean reservoir structure that might containhydrocarbons provides substantially no definite information. There maybe no hydrocarbons present in the reservoir structure, or none thatescape from the reservoir, or none that provide detectable amounts ofseepage through the relatively impermeable and hydrocarbon adsorptivelayer of mud that underlies the water.

A primary object of the present invention is to provide a relativelyeconomical and reliable procedure for detecting and characterizing anymobile reservoir fluids which have been adsorbed or otherwise trapped orentrained within a layer of unconsolidated sedimentary earth formationsunderlying a body of water.

SUMMARY OF THE INVENTION In accordance with this invention measurementsare made of the concentration of at least one mobile reservoir fluid ina water-covered unconsolidated sedimentary earth formation. A stream ofrelatively clean water is jetted into the sedimentary earth formation toform a pumpable slurry of sedimentary material in water. Measurementsare made of the locations at which the slurry is formed. And, gaseousfluid is extracted from the slurry and analyzed with respect to itsconcentration of a mobile reservoir fluid in order to map theconcentration with location of the mobile reservoir fluid in thesedimentary earth formation.

The present invention provides an improved method of exploring awater-covered region by: measuring the magnitude with location of atleast one geophysical property of subterranean earth formations;measuring the concentration with location within the water of at leastone mobile reservoir fluid; and, measuring the concentration withlocation within an unconsolidated sedimentary earth formation of themobile reservoir fluid in a region in which a geophysical property isindicative of a subterranean reservoir structure and the overlying wateris substantially devoid of the mobile reservoir fluid.

DESCRIPTION OF THE DRAWING FIG. I is a schematic illustration of asuitable system and its use in analyzing an unconsolidated sedimentaryearth formation in accordance with the present invention.

FIG. 2 is a more detailedillustration of water-jetting element for usein the system shown in FIG. 1.

FIG. 3 illustrates an alternative form of record.

FIG. 4 illustrates an alternative form of water-jetting element for usein the system shown in FIG. 1.

DESCRIPTION OF THE INVENTION In the equipment shown in FIGS. 1 and 2, avessel 1 is shown on a body of water 2, above a layer of unconsolidatedsedimentary earth formation or mud 3. A mud-sampling device 4 forms aslurry of sediment in water that is pumped to a surface location throughconduit 5. The mud-sampling device contains a pumping means 6 having anintake port 7, and a pump-discharge conduit 8. The pump-dischargeconduit is connected to jet nozzles 9 which are arranged to jet waterinto the mud to form a stream of slurry which flows into conduit 5 asshown by the arrows. The mud-sampling device 4 is mounted on a basestructure 10. As the mud-sampling device advances to increasing depthswithin the mud 3, a measuring means, such as a rack and pinionarrangement 11, responds to the extent of such advance and telemeters anelectrical signal relating to the depth of penetration by means ofelectrical conduit 14.

In a near surface location, the slurry of sedimentary solids in water ispumped through gas extractor l2 and discharged, as indicated at 12a. Theextracted gas is passed through a gas analyzer 13, and discharged, asindicated at 13a. An electrical signal from the gas analyzer is conveyedto recorder 15 by electrical conduit 16. The recorder may indicate, forexample, measurements made at each of a series of depths within thesediments 3 of the concentration of ethane and the concentration tototal hydrocarbon. As indicated in FIG. 3, such measurements can beutilized to plot the concentration with depth of such components of thesedimentary earth formation.

In the arrangement shown in FIG. 4, a slurry of sedimentary particles inwater is formed by a self-anchoring type of mud-sampling device. Pump 18is preferably a positive displacement pump, such as a Moyno pump that isadapted to pump a slurry into conduit 5 at a rate exceeding the rate ofwater inflow through intake port 19. In .such an operation, the pressureis reduced below base structure 10 and conduit 20 while water is jettedfrom the nozzles 9 into the mud 3 and the sampling device is urgedtoward the mud by the hydrostatic pressure of the body of water. Thissampling arrangement can be operated, for a selected time, such as atleast several minutes at each of a series of locations, so that, at'eachlocation, a substantially steady state flow of slurry of substantiallyuniform concentration is obtained. The maximum concentration during aselected time, or the average concentration during such a time, or thelike, is thus representative of the concentration of the mobilereservoir fluid being sampled at each location at which the samplingdevice is applied to the mud. Alternatively, such a sampling device canbe operated substantially continuously while being towed along thebottom of the body of water to measure a quantity such as concentrationwith distance along the line of tow.

In this invention the mobile subterranean reservoir fluid to be detectedcan comprise one or more of substantially any kind of mobile fluid thatis apt to seep out of a subterranean reservoir and migrate toward thesurface of the earth. Such fluids often comprise gaseous or relativelyvolatile hydrocarbons such as those containing from about one to tencarbon atoms, and/or one or more inorganic gases which are apt to becopresent with hydrocarbons in hydrocarbon containing reservoirs, suchas carbon dioxide, nitrogen, oxygen, hydrogen sulfide, etc.

The water which is jetted into the sedimentary earth formation to form aslurry of the sedimentary solids can be obtained from the body of wateror from substantially any convenient source ofa clean water which issubstantially free ofthe mobile reservoir fluid for which the sedimentis being analyzed. Where desirable, water from the body of water can bepreprocessed to remove contaminants and/or clean water can betransported from a supply source other than the body of water.

The pumping means for jetting the water into the mud andflowing theresulting slurry of sediments in water, or watery mixture of suspendedparticles, to a surface location can comprise one or more surface orsubsurface pumps and pump-driving devices. The rates of jetting thewater into contact with the mud, flowing the resultant slurry to surfacelocation, and advancing the stream of jetted water into the mud, arepreferably coordinated in order to maintain a relatively constant slurryconsistency with respect to the number of parts of suspended solid perpart of water.

In measuring the concentration of a mobile reservoir fluid with depthwithin the bottom sediments, a stream of jetted water is preferablyadvanced into the sediments by advancing a nozzle-supporting meansdownward past a base structure that rests on the top of a layer ofsediments while measurements are made of the magnitude with time of thatadvance.

At a convenient location near the surface of the body water, gas ispreferably extracted from the slurry by subjecting the slurry to aflashing or vaporizing action under-a relatively strong vacuum. Such agas extraction operation can be accomplished by means of known andavailable equipment and techniques such as those described in US. Pat.Nos. 2,918,579, 3,116,133, 3,296,776, 3,455,144, etc.

The gas which is extracted from the slurry is preferably supplied to achromatographic analyzer containing a chromatographic column adapted toisolate at least one individual component from the other components ofthe extracted gas. A flame ionization detector that is adapted toprovide an electrical signal related to the concentration of such a gasis preferably utilized to measure the concentration of the isolatedcomponent. Such gas analyzing devices are known and suitable types ofsuch equipment and techniques are described in the patents referred toabove. In a preferred procedure: a slurry of the bottom sediments isformed and pumped at coordinated rates, as mentioned above; gas isextracted substantially continuously from the slurry; and, aliquotportions of the extracted gas are supplied periodically to a gasanalyzer. Such a procedure facilitates the provision of a record of thetype shown in FIGS. 1 and 3 which indicates the concentration with depthwithin the mud. The extracted gas can advantageously comprise the vaporsof at least one hydrocarbon that contains at least four carbon atoms andmay be a liquid at normal atmospheric pressure and temperature. Themeasurements of the gas are preferably indicative of the concentrationsof at least one individual hydrocarbon.

higher than methane.

In a particularly preferred embodiment, such hydrocarbon measurementsare supplemented by measurements of at least one inorganic gas. Thecopresence of at least one hydrocarbon and at least one inorganic gas insignificant proportions provides a particularly significant indicationof the presence of an underlying reservoir that contains valuablepetroleum material.

The present invention is particularly useful in conjunction with othergeophysical and geochemical exploration processes that are applicable toa watercovered region. In an exploration process, it is generally tooexpensive to undertake all of the sampling and analyzing operationswhich would be needed to resolve all, or even most, of the questionsconcerning what might be contained in reservoirs below a largewater-covered region such as the Gulf of Mexico. Marine seismic and/orgravity measurements may indicate the presence of numerous anomaliesindicative of subterranean structures that might contain petroleummaterial. An analysis of water samples is apt to indicate that nohydrocarbon and/or inorganic gases indicative of seepage fromsubterranean reservoirs are present in the water in a region containingsuch an anomaly.

The present invention is at least in part premised on a discovery that,in the above-type of situation such inconsistent measurements may be dueto the low permeability and/or high fluid adsorptive properties ofunconsolidate sedimentary earth formation material underlying thatportion of the body of water. For example, in at least one region in theGulf of Mexico it was found that seismic anomalies and other geologicalinformation were indicative of subterranean reservoirs that were apt tocontain hydrocarbons, but no hydrocarbons could be detected in samplesof the water in measurements made in a manner that was adapted to detectless than one part per million. In the same region, when the underlyingbottom sediments were analyzed in accordance with the present reservoirthey were found to contain significant concentrations of totalhydrocarbons and ethane. In the same region it was established that thesubterranean reservoir which was responsible for the appearance of theseismic anomaly was an oil-containing reservoir.

We claim as our invention:

1. In a process for surveying a water-covered region by measuringconcentrations of at least one mobile reservoir fluid in water-coveredunconsolidated sedimentary earth formations at known areal locations, animproved procedure that provides a measurement of the concentrationswith depth within the formations, comprising:

jetting a stream of water into contact with a water coveredunconsolidated sedimentary earth formation at increasingly deeper depthswithin the formation to form a pumpable slurry of the sedimentarymaterial in water;

flowing said slurry to a surface location;

coordinating the rate at which said water .is jetted, the rate at whichthe depth at which said slurry is formed is advanced deeper within theearth formation and the rate at which said slurry is flowed to a surfacelocation in order to maintain a substantially constant slurryconsistency;

measuring a quantity related to the depth within said sedimentary earthformation at which said slurry is formed; and

extracting gas from said slurry and measuring a quantity related to theconcentration with depth within said sedimentary earth formation of atleast one mobile subterranean reservoir fluid.

2. The process of claim 1 including:

measuring the magnitude with areal location of (a) at least onegeophysical property responsive to subterranean earth formations and (b)the concentration of said at least one mobile subterranean reservoirfluid; with said measurements being conducted in a region in which thewater is substantially devoid of said mobile subterranean reservoirfluid but said measured geophysical properties of the subterranean earthformations are indicative of the presence of a subterranean adapted tobe a reservoir.

3. The process of claim 2 in which said geophysical property is thereflection of seismic energy.

4. The process of claim 3 in which said mobile subterranean reservoirfluid is a hydrocarbon higher than methane.

5. The process of claim 1 including measuring the concentration of atleast one hydrocarbon higher than methane and at least one inorganicgas.

6. The process of claim 1 including measuring maximum concentration ofsaid mobile fluid that is extracted within a selected depth intervalwithin said sedimentary earth formation. 1

7. The process of claim 1 including measuring the average concentrationof said mobile fluid that is extracted within a selected depth intervalin said sedimentary earth formation.

8. The process of claim 1 including measuring the concentration of saidmobile fluid with location along the upper boundary of said sedimentaryearth formation.

1. In a process for surveying a water-covered region by measuringconcentrations of at least one mobile reservoir fluid in water-coveredunconsolidated sedimentary earth formations at known areal locations, animproved procedure that provides a measurement of the concentrationswith depth within the formations, comprising: jetting a stream of waterinto contact with a water-covered unconsolidated sedimentary earthformation at increasingly deeper depths within the formation to form apumpable slurry of the sedimentary material in water; flowing saidslurry to a surface location; coordinating the rate at which said wateris jetted, the rate at which the depth at which said slurry is formed isadvanced deeper within the earth formation and the rate at which saidslurry is flowed to a surface location in order to maintain asubstantially constant slurry consistency; measuring a quantity relatedto the depth within said sedimentary earth formation at which saidslurry is formed; and extracting gas from said slurry and measuring aquantity related to the concentration with depth within said sedimentaryearth formation of at least one mobile subterranean reservoir fluid. 1.In a process for surveying a water-covered region by measuringconcentrations of at least one mobile reservoir fluid in water-coveredunconsolidated sedimentary earth formations at known areal locations, animproved procedure that provides a measurement of the concentrationswith depth within the formations, comprising: jetting a stream of waterinto contact with a water-covered unconsolidated sedimentary earthformation at increasingly deeper depths within the formation to form apumpable slurry of the sedimentary material in water; flowing saidslurry to a surface location; coordinating the rate at which said wateris jetted, the rate at which the depth at which said slurry is formed isadvanced deeper within the earth formation and the rate at which saidslurry is flowed to a surface location in order to maintain asubstantially constant slurry consistency; measuring a quantity relatedto the depth within said sedimentary earth formation at which saidslurry is formed; and extracting gas from said slurry and measuring aquantity related to the concentration with depth within said sedimentaryearth formation of at least one mobile subterranean reservoir fluid. 2.The process of claim 1 including: measuring the magnitude with areallocation of (a) at least one geophysical property responsive tosubterranean earth formations and (b) the concentration of said at leastone mobile subterranean reservoir fluid; with said measurements beingconducted in a rEgion in which the water is substantially devoid of saidmobile subterranean reservoir fluid but said measured geophysicalproperties of the subterranean earth formations are indicative of thepresence of a subterranean adapted to be a reservoir.
 3. The process ofclaim 2 in which said geophysical property is the reflection of seismicenergy.
 4. The process of claim 3 in which said mobile subterraneanreservoir fluid is a hydrocarbon higher than methane.
 5. The process ofclaim 1 including measuring the concentration of at least onehydrocarbon higher than methane and at least one inorganic gas.
 6. Theprocess of claim 1 including measuring maximum concentration of saidmobile fluid that is extracted within a selected depth interval withinsaid sedimentary earth formation.
 7. The process of claim 1 includingmeasuring the average concentration of said mobile fluid that isextracted within a selected depth interval in said sedimentary earthformation.